Acrylic acid is a chemical for which the worldwide demand is high, about 5 Mt/a (million ton per annum) in 2008 and possibly about 9 Mt/a by 2025. A known route for the production of acrylic acid comprises the oxidation of propene into acrolein (propenal) and then oxidation of the acrolein into acrylic acid. See for example “On the partial oxidation of propane and propene on mixed metal oxide catalysts” by M. M. Bettahar et al. in Applied Catalysis A: General, 145, 1996, p. 1-48. The overall reaction stoichiometry for this route is as follows:CH2═CHCH3+1.5O2→CH2═CHCOOH+H2O.
A disadvantage of the above-mentioned route for the production of acrylic acid is that two oxygen atoms have to be introduced into the propene by the use of an oxygen containing gas at high temperature (about 350° C.) and with release of a large amount of heat (about 600 kJ/mol). A further disadvantage is that propene has to be used which may be derived from propane. Both propene and propane are currently only readily available as fossil feedstocks and are therefore not renewable.
U.S. Pat. No. 3,855,279 discloses a process for the conversion of propanoic acid to acrylic acid.
S. Sato, et al., Applied Catalysis A: General, 2008. 347(2), 186 teaches a method for conversion of 1,3-propanediol to propanoic acid. However, the same paper teaches that monopropylene glycol is converted mostly to hydroxyacetone under the same conditions, with only a very little propanoic acid formed as a by-product.
In addition to acrylic acid, monoethylene glycol is also a chemical for which the worldwide demand is high, about 20 Mt/a (million ton per annum) in 2008. Monoethylene glycol may be advantageously produced from sugar sources, such as sucrose, glucose, xylose or fructose and the corresponding polysaccharides, cellulose, hemicellulose, starch and inulin. A disadvantage of this route is that in addition to monoethylene glycol, also a lot of monopropylene glycol is formed. It may even be the case that two to three times more monopropylene glycol is formed than monoethylene glycol. See for example “Hydrogenolysis Goes Bio: From Carbohydrates and Sugar Alcohols to Platform Chemicals” by Agnieszka M. Ruppert et al. in Angew. Chem. Int. Ed., 2012, 51, p. 2564-2601.
In contrast to acrylic acid and monoethylene glycol, the worldwide demand for monopropylene glycol is not high, about 1.5 Mt/a (million ton per annum) in 2008. Currently, it is estimated that the worldwide demand for monoethylene glycol is ten times higher than that for monopropylene glycol. Because of this lower demand for monopropylene glycol, processes for converting sugar sources into monoethylene glycol may not be commercialized, unless the selectivity to monoethylene glycol would be drastically increased. Such selectivity increase is difficult to achieve. Consequently, there is currently a need in the art to valorize the monopropylene glycol that is automatically formed when transforming sugar sources into monoethylene glycol. A desired valorization could be an application wherein the monopropylene glycol is converted into a chemical for which the worldwide demand is high.
The above-mentioned monopropylene glycol is just one example of a C3-oxygenate. C3-oxygenates contain 3 carbon atoms and 1 or more oxygen atoms. There are also C3-oxygenates other than monopropylene glycol, which may contain 1, 2 or 3 oxygen atoms and which may also be formed as undesired (by)products in certain production processes such as biomass conversion processes. Such biomass conversion process may be the aqueous phase reforming of sugars, as disclosed by N. Li et al. in Journal of Catalysis, 2010, 270, p. 48-59. Examples of such other C3-oxygenates are:
1-propanol, monohydroxyacetone, 2-hydroxypropanal glycerol and dihydroxyacetone.
Consequently, there is a need in the art to valorize C3-oxygenates in general, such as for example monopropylene glycol or glycerol, which may be formed as undesired (by)products in certain production processes such as biomass conversion processes.